The quality of a call carried over a telecommunication network will be dependent upon a variety of factors. Take for example the case of a voice call carried over a telecommunications network. The voice quality, as perceived by a listener at an end user terminal, will be dependent upon both terminal properties and properties of the network. In the case of a call involving a wireless terminal, quality will also be dependent upon the qualities of the radio link(s).
Mobile terminal manufacturers strive to introduce into their terminals components and functionality to produce optimal call quality, so-called Voice Quality Enhancement (VQE) functions. These might include Mobile Crosstalk Control (echo cancellation) and Noise Reduction functions. However, VQE functions will inevitably impact on the cost of terminals with the result that low end terminals may provide poorer quality performance than high end terminals.
In an attempt to provide a more uniform quality of service to users, network operators can introduce into their network some of the VQE functions. In the case of a mobile network, this may be done at a Mobile Switching Centre (MSC) or at a Media Gateway, or integrated into network echo cancellers on TDM trunks. Such network based VQE functions may operate on coded or uncoded data. Of course, a VQE function may not be required for certain terminals (indeed most terminals), but the processing load placed on a network element to determine, on a per-call basis, when a VQE function is required can still be very high. When such a per-call VQE feature is implemented, the processing capacity of a node may drop by 30 to 40%.
It has been proposed to invoke network based VQE functions based upon user subscriptions or subscriber terminal types. However, the former is problematic because users may change their terminals at fairly regular intervals. The latter is problematic because it may not be possible for the network to maintain an up-to-date database of terminal types and respective VQE functions, and because it may not be possible for a terminal to signal its type to the network.